1. Field of the Invention
The present invention relates to a radio communication apparatus using a frequency hopping method for switching a hopping carrier frequency to be used in accordance with a predetermined hopping pattern and an interference avoiding method.
2. Description of the Related Art
In recent years, in an ISM band (for industrial scientific medical treatment) having a 2.4 GHz band, various apparatuses including a microwave oven are used and the frequency band is apt to cause the problem of a radio wave interference between the apparatuses. For this reason, there have been employed means for avoiding a radio wave interference by utilizing a spectrum diffusing technique using a direct diffusing method which is represented by a radio LAN and a spectrum diffusing technique (FHSS) using a frequency hopping method which is represented by Bluetooth.
Moreover, various apparatuses use the ISM band having the 2.4 GHz band and an interference is apt to be generated in the frequency band. The spectrum diffusing technique using a frequency hopping method is comparatively resistant to a disturbance. Also in the case in which a communication is to be carried out in the ISM band, the frequency hopping method carries out hopping into a specific carrier frequency thereof in a constant cycle, resulting in the receipt of an interference if an interference source for continuously carrying out generation for a comparatively long time at a frequency overlapping with a certain carrier frequency (hereinafter referred to as a carrier frequency).
For example, as described in JP-A-7-107010, there has been proposed an adaptive frequency hopping method for changing a hopping pattern to avoid an interference.
A specific operation will be described below with reference to FIG. 14. FIG. 14 is a diagram showing the structure of a conventional adaptive radio communication apparatus using a frequency hopping method.
The conventional radio communication apparatus shown in FIG. 14 has a frequency slot switching portion 104 for sequentially switching a frequency slot (a carrier frequency) in accordance with a frequency hopping pattern. In the frequency slot switching portion 104, observing means 110 observes the state of the receipt of the frequency slot which is being used as a frequency hopping pattern. When receiving the transfer of a state which can be an obstacle by the observing means 110, hopping pattern changing means 111 deletes the frequency slot (the carrier frequency) from a hopping pattern table 113 and adds a spare unused carrier (a spare carrier) to the hopping pattern table, and furthermore, outputs the changed contents to a transmission data transfer path 105 in order to transfer the same contents to a communication partner by utilizing a transmission free time. Consequently, the hopping patterns to be used for a communication are modified mutually, thereby implementing the avoidance of an interference.
In the method of changing a hopping pattern to avoid an interference as described in the Patent Document 1 including a method of hopping a carrier frequency in accordance with a predetermined hopping pattern, however, there is a problem in that a certain time is required until a change to an optimum hopping pattern is carried out after the start of a communication, and an interference might be caused during that time.
(The invention avoids an interference quickly)
However, a radio environment is changed during a communication. For this reason, there is a possibility that some carrier frequencies might be subjected to the interference of a disturbance wave during that time. If the carrier frequency which is once removed as a spare carrier from a hopping pattern by the interference is maintained to be unused, usable spare carriers are gone when the same number of carries as that of the spare carriers in total from the start of the communication are exchanged, and the carriers cannot be then exchanged. Consequently, it is hard to hold quality of the communication.
(The invention restores a spare carrier)